The present invention relates to plasma display panels, display apparatuses using the same and their driving methods, especially to the display panels which have unconventionally high luminance and emission efficiency.
Plasma display panel(PDP)s have faster displaying speed, wider visual field, are easier in enlarging the size, and, since they emit light by themselves, better picture quality than liquid crystal displays (LCD) is obtained. Due to these characteristics, among flat panel display technologies, they are attracting special attention. In general, in PDP technology, ultraviolet rays are generated by gas discharge. The UV rays excite the phosphor to emit light to display color image. Display pixels (pixels) which are divided by ribs, are disposed on substrates. The phosphor layer is formed in the display pixels. The current main PDPs are three-electrode surface discharge type PDPs.
FIG. 58 shows a perspective exploded view illustrating the construction of a conventional three-electrode surface discharge type PDP. As FIG. 58 shows, the conventional PDP has pairs of display electrodes comprising a scan electrode 1 and a sustain electrode 2 placed closely and in parallel with each other on one of the substrates. Address electrodes 3 extending transversely to the display electrodes and ribs 16 and a phosphor layer 17 are disposed on the other substrate. This construction allows the phosphor layers to be comparably thicker, thus suitable for color displays.
As a discharge between the electrode 1 and 2 emits light which displays the image, it is called a sustain discharge, or, since it occurs in parallel with a substrate 10, it is called a surface discharge. A dielectric layer 4 is formed on the electrodes, and for protection, it is coated with a protective layer 5 made of MgO. Space charge of electrons and cations ionized by discharge is accumulated on the dielectric layer 4. This space charge is called xe2x80x9cwall chargexe2x80x9d. In PDPs, the voltage of the wall charge and the voltage applied from outside control the discharge.
The electrodes 1 and 2 are transparent electrodes, and they output light emitted at their bottom outside of the substrate 10. A plurality of electrodes 3 are disposed transversely perpendicular to the electrodes 1 and 2. An address discharge that selects the pixels to emit light for displaying, occurs between the electrodes 3 and the electrode 2. The address discharge is also called transverse discharge since it occurs perpendicularly between the substrate 10 and substrate 20. R, G and B phosphor 8 are disposed on the electrodes 3. To prevent the colors of the phosphor 8 from mixing, ribs 16 are placed parallel to the electrodes 3.
In a conventional driving method of a PDP, one field period is divided into a plurality of sub-fields, and by combining these sub-fields graduation is displayed. Each sub-field comprises a setup period, an address period, a sustain (display discharge) period and an erase (discharge termination) period.
To display image data, different signal waveforms determined by the setup, address and sustain periods, are applied on each of the electrodes. During the setup period, setup pulses are applied on all of the electrodes 1.
During the address period, writing pulses are applied between the electrodes 3 and the electrodes 1 to make address discharge and to select discharge pixels.
In the following sustain period, cyclical sustain pulses which are inverted alternatively are applied between the electrode 1 and the electrode 2 for a predetermined period to make the sustain discharge between the two electrodes and to display images.
Finally, during the erase period, a weak discharge is generated to remove unevenness of the wall charge between pixels caused by the discharge during the sustain period. Then, the same process is repeated in the following sub-field.
However, the plasma display devices using the conventional PDPs have problems of low emission efficiency and low luminance. For example, the emission efficiency is 11 m/W, which is only a fifth of that of CRT display devices.
The reason for this low efficiency is that in the case of PDPs, the strength of emission obtained at each discharge is virtually the same, and the luminance is low. In one field period, there are the startup and address periods that do not contribute to the emission but occupy more than half of one field period. To intensify the luminance of the display within a limited time, sustain pulses should be increased. As a result, frequency and cycle of the sustain pulses of the conventional PDPs are set to be about 200 KHz and 5 xcexcs respectively.
The sustain pulses have startup time and terminating time, and PDPs are capacitive loads. Circuit which collect ineffective power associated with charging and discharging of the sustain pulse require about 500 ns each. Furthermore, in the first 200 ns after the starting up of the sustain pulses, discharge does not occur due to a statistical delay. And, there is discharge sustaining time lasting about 1 xcexcs. Therefore, it is difficult to improve the luminance of the screen with the conventional PDPs by increasing frequency of the sustain pulses further.
In the case of high definition panels, which is expected to enjoy increasing demand, the ribs that partition pixels increases in terms of their proportion on the display. The ribs do not contribute to the light emission, therefore, emissive area decreases, lowering the luminance of the display.
A lot of effort has been made to solve the problems mentioned above. In one effective method, positive column is used to enhance the emission efficiency of the UV rays. However, no PDPs adopting this method have been commercialized yet.
The possible reasons for this are:
a) distance between electrodes necessary to generate positive column can not be obtained since the sizes of the pixels of PDPs are limited, and
b) discharge can not be stabilized only by expanding the distance between electrodes, because it is difficult to control the discharge. Related patents to the foregoing method are Japanese Patent Laid Open Unexamined Publication No. H05-41165, Japanese Patent Laid Open Unexamined Publication No. H05-41164, and Japanese Patent Laid Open Unexamined Publication No. H06-275202. However, all of them have failed to achieve satisfactory results.
The present invention aims to provide PDPs, their display devices and driving methods of the same which achieve a stable use of the positive column, high luminance and high emission efficiency.
The PDP of the present invention comprises:
a first substrate on which first and second electrodes are disposed;
a second substrate on which third electrodes are disposed transversely to the first and second electrodes, and which, together with the first substrate, sandwiches the discharge space;
ribs dividing the discharge space into emission units (EU); and
phosphor layer.
Further, protrusions shorter than the ribs are disposed between the first and second electrodes.
Another PDP of the present invention has a first substrate having first and second electrodes thereon. On the first substrate, third electrodes are also disposed transversely to the first and second electrodes at right angles, via a dielectric material.
The intervals between the first and second electrodes are 0.2 mm or more. A plurality of third electrodes is disposed in a EU. Protrusions shorter than the ribs are disposed between the plurality of the third electrodes. The protrusions are disposed in parallel with the third electrodes in such a manner that they form stripes. The plurality of third electrodes is connected to each other or connected such that they form a network at least in part.
A plurality of fourth electrodes (float electrode) is formed between the neighboring first and second electrodes. At least a part of the float electrodes is connected to one another.
The intervals between the first and second electrodes are 0.2 mm or more, longer than that of neighboring ribs. In between the neighboring first and second electrodes is part of the ribs.
The driving method of the PDP of the present invention includes;
generating self-erasing discharge (self-erasing discharge here means a discharge which is generated by its own wall charge when a potential between electrodes is reduced) in the PDP having at least three different kinds of electrodes (first, second and third electrodes); and then
generating discharge and emitting light using the self-erasing discharge as a trigger when a potential difference between the electrodes is increased.
Another driving method of the PDP of the present invention includes:
producing a potential difference between the first and second electrodes, the first and third electrodes and/or the third and second electrodes;
putting discharge current (I main) to flow to emit light between the first and second electrodes;
applying counter electromotive force (Vemf-main) which suppresses fluctuation of the discharge current to the first electrode and/or the second electrode; and
putting discharge current (I sub) to flow between the third and second electrodes and/or the first and third electrodes.
With yet another driving method of the present invention, sustain pulses are applied to the third electrodes on the second substrate when the sustain discharge occurs between the first and second electrodes on the first substrate, and a sustain discharge is generated between one of the first and second electrodes or both of them and the third electrodes.
By driving the PDP of the present invention by the driving method of the present invention, positive column discharge is generated firmly, suppressing flickering of the discharge of the plasma display device. Since the self-erasing discharge can be used as a trigger discharge, the positive column discharge of the following cycle can be triggered at low voltages. Further, stable sustaining of the discharge becomes possible.
The positive column discharge produced in the foregoing manner, is remarkably efficient, realizing strong emission. Furthermore, the positive column discharge of the following cycle can be generated at low voltages. In addition, in the case of PDP in which a phosphor layer is formed on the third electrodes, degradation of the phosphor layer can be decreased.
Part of the discharge occurring near the first substrate occurs near the second substrate as well. Therefore, ultraviolet rays move toward the second substrate, increasing light emitted from the phosphor near the second substrate and increasing the luminance of the screen of the PDP. Further, power consumption is reduced.
When all of the three electrodes are formed on the same substrate, materials with a high secondary emission coefficient can be used as a protective layer. This allows starting voltages of the PDP to be lowered.
By forming float electrodes in between the neighboring pixels (minimum display unit), cross-talk can be reduced.
With the present invention, potentials of the first, second and third electrodes are set the same during the erase period. This allows metastable atoms generated by crashing of atoms and residual space charge in the discharge space to be accumulated as wall charge, suppressing mis-discharge. Further, when fourth electrodes are added, residual space charge during the discharge period can be accumulated in the fourth electrodes to prevent its diffusion to other discharge spaces, enabling discharge control. These constructions allow the PDP to have high emission efficiency and to select any pixels when widening the distance between the first and second electrodes.